Why does the satin fabric appear so metallic to me while it is a dielectric material
The theory I had seems to be correct: the light bounces in the ridges of the fabric and give the gloss a color toward the diffuse.  We cannot simulate this in blender with a bumpmap or a normalmap. So I did an experiment with real geometrie.  Here two illustrations. First illustration shows that we cannot achieve this with a bumpmap. Second illustration shows that we can achieve this in blender only with real geometrie and enough light bounces.